Process for optimum absorption of elemental sulfur from natural gas by the use of mineral oil and similar liquid hydrocarbons

ABSTRACT

Natural gas containing elemental sulfur dissolved therein is freed of the sulfur by introducing an ascending annular current of a mineral oil into an ascending flow of natural gas. The mineral oil has a viscosity of 2-200 cP and a vapor pressure of up to 3 X 10 1 mm Hg at 20*C. The sulfur is transferred from the natural gas into the mineral oil. To insure substantially complete transference, the ratio of mineral oil in liter/hr to natural gas in Nm3/hr should be maintained at 1: about 4-20.

United States Patent Bulian et a1. July 31, 1973 PROCESS FOR OPTIMUM ABSORPTION OF [56] References Cited ELEMENTAL SULFUR FROM NATURAL UNITED STATES PATENTS GAS BY THE USE OF MINERAL AND 3,474,028 10/1969 Bulian et al 208/230 SlMILAR LIQUID HYDROCARBONS 3,097,917 7/1963 Dotts, Jr. et al. 55 73 [75] Inventors: Walter Bulian; Armin Dittmar, both of Barnstorf, Germany Wintershall Aktiengesellschaft, Kassel, Germany Filed: Nov. 25, 1970 App]. No.: 92,633

Assignee:

[30] Foreign Application Priority Data Nov. 28, 1969 Germany P 19 59 827.7

U.S. Cl. 55/73, 208/230 Int. Cl 801d 53/16, C10g 19/02 Field of Search 55/68, 73; 23/3,

Primary Examiner-Charles N. Hart Attorney-Waters, Roditi, Schwartz & Nissen [57] ABSTRACT 13 Claims, 2 Drawing Figures INJECTION PUMP N-su-rnm SURGE TANK I 20 .2. rum/ 14 1 2 PRESSURE (I PUMP (REACTION ssrmmou SEPARATOR 15 TANK 1a TANK 2! NATUML GAS RESERVOIR PROCESS FOR OPTIMUM ABSORPTION OF ELEMENTAL SULFUR FROM NATURAL GAS BY THE USE OF MINERAL OIL AND SIMILAR LIQUID HYDROCARBONS SUMMARY OF THE INVENTION According to the invention, natural gas containing large amounts of elemental sulfur in the vapor phase is freed therefrom by introducing into a rising stream of natural gas, an ascending, annular current of a mineral oil or a similar liquid hydrocarbon. The mineral oil may be diesel oil, spindle oil or light machine oil; and the liquid hydrocarbon may be benzene, toluene xylene, coal tar oil, etc. The only requirement is that the mineral oil or hydrocarbon have a viscosity of 2200 cP at 20C., and a vapor pressure of up to 3 X l mm Hg at 20C. The annular flow of mineral oil or liquid hydrocarbon surrounds the rising flow of natural gas and completely wets the casing wall.

For a well delivering l,000-40,000 Nm lhr of natural gas, there are added 200-4,000 liters/hr of the mineral oil, while maintaining the ratio of mineral oil in l/hr to natural gas in Nm lhr at 1: about 4-20.

BRIEF DESCRIPTION OF THE DRAWING:

FIG. 1 is a schematic representation of the apparatus of the invention.

FIG. 2 is a schematic representation of a second embodiment of the apparatus.

DETAILED DESCRIPTION:

According to the present invention, there has now been found a process for the optimum absorption of elemental sulfur from natural gas by the use of mineral oil and similar hydrocarbons, which safely avoids the difficulties of the known processes and is practicable even with high sulfur content over 1 gm of sulfur per Nm and even as high as 5 gm of sulfur per Nm of natural gas.

The process comprises introducing into a rising column of natural gas (i.e., rising from a well bottom), an ascending annular current of a mineral oil fraction or similar liquid hydrocarbon having a viscosity of 2200, preferably -60 of at C. and a vapor pressure up to 3 X 10 mm Hg at 20C. running up the pipe wall in the two-phase system consisting of mineral oil fraction or liquid hydrocarbon and the natural gas having elemental sulfur dissolved therein in the vapor phase.

The mineral oil fraction may be any one of diesel oil, spindle oil, light machine oil, or any other mineral oil having the stated viscosity and vapor pressure. The liquid hydrocarbon which may be used in place of the mineral oil may be benzene, toluene, xylene, coal tar oils, etc, so long as it meets the vapor pressure and viscosity requirements set forth above.

In order to achieve a thorough transfer of the elemental sulfur from the natural gas to the mineral oil fraction, about 200-4,000 liters/hr, preferably SOD-1,000 liters/hr of the mineral oil fraction are fed in at the well bottom into an ascending stream of natural gas coming up at the rate of 1,000-40,000 Nmlhr and preferably at 5,000-l5,000 Nin /hr, while maintaining the ratio of mineral oil fraction (liters/hr) to natural gas (Nmlhr) at 1: about 4-20.

If the ratio of the mineral oil fraction to the natural gas falls to less than I 2, no annular current is obtained and complete transfer of elemental sulfur from the natural gas to the mineral oil fraction does not take place. Therefore, complete desulfurization of the natural gas is not achieved, nor is the danger of choking the riser with sulfur eliminated.

If the ratio of the mineral oil fraction to the natural gas exceeds approximately I 4 a blockage in flow occurs which results from a building up of individual slugs of oil in the gas stream, which, on account of their small surface area cannot guarantee the optimum desulfurization of the natural gas.

Although the ratio of mineral oil (liters/hr) to natural gas (Nm lhr) is in the range of I: about 4-20, the amount of sulfur present in the natural gas will determine more precisely the ratio. Thus, in order to initiate the necessary annular flow, at a mean hydraulic pressure of about 150-500 atmospheres pressure with an ascending natural gas flow of about 10,000 Nm lhr having a sulfur content up to approximately 0.1 gm/Nm the ratio of mineral oil fraction (liters/hr) to natural gas (Nm lhr) should be approximately 1 20; when the sulfur is present in amounts from 0.1 to l gm/Nm the ratio should be I 12; when the sulfur is present in amounts from I to 2 gm/Nm, the ratio should be I 8 and when the sulfur is present in amounts from 2 to 5 gm/Nm, the ratio should be I z 4.

According to a further aspect of the invention, in order to accelerate the complete transfer of the sulfur from the natural gas to the mineral oil fraction, a surface-active agent, preferably a fatty amine having the formula CH -(CI-I,),,-CI-I -NH, or the hydrochloride thereof, wherein n is an integer from 6 to 20 such as stearyl amine, is added thereto in order to reduce the interfacial tension between the natural gas and the mineral oil fraction in amounts ranging from about to 2,000, preferably 300 to 1,000 parts per million. According to a still further aspect of the invention, in order to reuse the mineral oil fraction, the sulfur physically dissolved therein as a result of the transfer is removed by desulfurization using a liquid-liquid extraction with a l-l0 percent, preferably 25 percent aqueous, alkali-hydrogen sulfide solution such as a solution of NI LHS and/or NaI-IS. For speeding up the transfer of the sulfur dissolved in the mineral oil fraction to the aqueous solution, surface-active media such as an ionic and/or a nonionic hydroxyalkylate, for example, from a glycol and an alkylene oxide or sulfo acids from esters of oxygenic and nitrogenous organic base molecules in amounts from approximately l002,000, preferably SOD-1,200, ppm are added to the alkalihydrogen sulfide solution. The preferred surface-active medium is SeparoP', a product of BASF which is a polyethylenepropylene oxide having a molecular weight between 2,000 and 5,000.

In the drawing, in FIG. 1, the riser pipe 10 of a natural gas well delivering natural gas from gas reservoir 11 is connected, at the well bottom, with a second parallel or concentric line 12 for feeding mineral oil into an ascending stream of natural gas coming up from the well bottom under pressure. Pipe 12 is provided with an injection flow regulator 13 through which the mineral oil coming down line 12 is introduced beneath packing 25 into the space 24 within which lines 10 and 12 both open. From space 24, the mineral oil trickles downward toward the opening of line 10 where it is entrained in the ascending stream of natural gas. At the well head 14, the natural gas mixed with mineral oil is led to high pressure separator 15 wherein the natural gas is separated from the mineral oil. Natural gas, free of mineral oil and sulfur is removed via conduit 16 and the mineral oil containing sulfur is led via conduit 17 to closed tank 18 into which is fed via conduit 19, an aqueous solution of NaHS for aiding in the removal of the sulfur from the mineral oil by a liquid-liquid extraction. The two phase mixture of mineral oil and aqueous NaHS solution is led via conduit 20 to separation tank 21 in which the two phases are separated by gravity. The oil phase, free of sulfur is recycled, via conduit 22 to conduit 12 for reuse. The aqueous phase is discarded via conduit 23.

In FIG. 2 there is shown a second embodiment wherein the second line 12 is concentrically disposed with relation to riser pipe 10.

The process of the invention is further illustrated by Examples 1 and 2:

EXAMPLE 1 In a natural gas well delivering 10,000 Nm lhr and containing 6 percent of hydrogen sulfide and 1 gm/Nm of elemental sulfur dissolved in the gas, a mineral oil fraction of 12 cl viscosity at 20C. and a vapor pressure 2.4 X 10 mm Hg at 20C is measured in through an injection flow regulator 13 from a second line 12 in the well bottom.

The bottom hole temperature which amounted to 125C. establishes a temperature of about 80C. for the mineral oil fraction after the inflow at the well bottom.

The amount of the mineral oil fraction added comes to 800 l/hr and said fraction contains an initial 0.45 percent by weight of sulfur.

in order to accelerate complete transfer of the sulfur from the natural gas to the mineral oil fraction, a fatty amine, like stearyl amine in an amount of 1,000 ppm was added to the mineral oil fraction before introducing same into the flow of natural gas.

At this rate of discharge, the ratio of mineral oil fraction (llhr): gas (Nm lhr) came to about 1 12.5, with the average well flow pressure being about 300 atmospheres.

By maintaining this set ratio of mineral oil fraction to the natural gas, an ascending annular current of the mineral oil fraction rising up the riser string wall 10 was instituted in the two-phase oil and natural gas system.

On leaving the well head 14, the mixture of mineral oil fraction and natural gas is separated by means of a high-pressure separator 15. The natural gas issues from the separator practically free of elemental sulfur and mineral oil and after drying, the natural gas is taken for further processing or for use.

The mineral oil fraction is then flashed to atmospheric pressure and delivered to a closed tank 18. This mineral oil fraction contains 1.90 percent sulfur by weight, which is removed from the mineral oil fraction by a liquid-liquid extraction with a NaHS solution down to a residual content of 0.5 percent by weight of organi cally combined sulfur. The nature of the organically combined sulfur in the mineral oil fractions differs and depends on the source and manner of processing of the crude oil. The NaHS solution is produced for example by introducing sour gas into a NaOl-l solution.

For the extraction, an aqueous sodium hydrogen sulfide solution of 2.5% NaHS is used, to which a nonionic hydroxyalkylate prepared from glycol and an alkylene oxide is added in proportions of 1,000 ppm as a surface-active agent for speeding and more perfect transfer of the elemental sulfur from the mineral oil phase to the aqueous phase.

The two liquid phases of mineral oil fraction and NaHS solution in which the surface-active agent is dissolved are mixed homogeneously together by pumping with a centrifugal pump to effect a quicker and more perfect transfer of the sulfur from the mineral oil fraction to the aqueous phase.

Of the mineral oil fraction, 5 m containing 1.9 percent by weight of sulfur is scrubbed with l m of the 2.5% NaHS solution and is thus freed of sulfur. The sulfur scrubbed out of the mineral oil fraction reacts with the sulfur and the NaHS solution to form a sodium polysulfide of the type Na,S, wherein x=2 to 5.

The mixture is conveyed to another tank 21, in which separation of the two phases is automatically and perfectly completed by gravity separation. After about 3 hours, the oil is free of the sulfur and water and is recycled again into circulation.

EXAMPLE 2 In a natural gas well delivering 15,000 Nm lhr of natural gas at a hydraulic pressure of 325 atmospheres and containing 1.65 gni/Nm of elemental sulfur in addition to 7.5 percent of H 8 dissolved in the gas, 1,500 liters of spindle oil are injected in order to dissolve the sulfur. After separation of gas and oil at the wellhead by means of a separator, the oil contains 16.5 gm/l of dissolved sulfur. To free the oil of the sulfur and to enable it to be again usable for recycling 3 m of oil are scrubbed with m of a 2.5 percent aqueous NaHS solution and thus freed of sulfur.

What is claimed is:

1. In a process wherein natural gas containing elemental sulfur in the vapor phase ascends from a well bottom through a riser pipe at the rate of LOGO-40,000 Nm lhr, the steps comprising introducing, at the well bottom, a stream of mineral oil or liquid hydrocarbon having a viscosity of 2-100 cP at 20C and a vapor pressure of up to 3 X 10"mm l-lg at 20C in an amount of 200 to 4,000 liters/hr and containing about 1,000 ppm of 2 fatty amine with the proviso that the ratio of mineral oil or liquid hydrocarbon, in terms of liters/hr to the natural gas, in terms of Nm lhr be maintained at l to about 4-20 to effect an ascending annular current of said mineral oil or liquid hydrocarbon circulating in the two phase system consisting of natural gas and said mineral oil or liquid hydrocarbon, the elemental sulfur in said natural gas being completely absorbed in said mineral oil or liquid hydrocarbon as a result of said circulating current and thereafter separating the natural gas from the mineral oil or liquid hydrocarbon having sulfur dissolved therein.

2. A process as claimed in claim 1 wherein the natural gas ascends from the well bottom at the rate of 6. A process as claimed in claim 1 wherein the natural gas contains as much as 5 gm of elemental sulfur per Nm".

7. A process as claimed in claim 1 wherein the natural gas ascends from the well bottom at the rate of about 10,000 Nm lhr at a mean gas flow pressure of about 150-500 atm and the ratio of mineral oil to natural gas is about 1 to 20 when the natural gas contains up to about 0.1 gm of elemental sulfur per Nm the ratio is about 1 to l2 when the natural gas contains about 0.1 to 1.0gm of elemental sulfur per Nm"; the ratio is about 1 to 8 when the natural gas contains about 1 to 2 gm of elemental sulfur per Nm and the ratio is about 1 to 4 when the natural gas contains about 2 to Sgm of elemental sulfur per Nm.

8. A process as claimed in claim 1 which further comprises desulfurizing the mineral oil or liquid hydrocarbon by a liquid-liquid extraction with a l to percent aqueous alkali-hydrogen sulfide solution in the presence of l002,000 ppm of a surface active agent for accelerating the transfer of the sulfur from the mineral oil or liquid-hydrocarbon to the aqueous phase and recycling the desulfurized mineral oil or liquid hydrocarbon.

9. A process as claimed in claim 8 wherein the aqueous alkali hydrogen sulfide solution has concentration of 2 to 5 percent and 500-1 ,200 ppm of the surface active agent are used.

10. A process as claimed in claim 9 wherein the alkali hydrogen sulfide is NH H'S and/or NaHS and the surface active agent is an ionic or nonionic hydroXylakylate based on a glycol and an alkyleneoxide or a sulfo acid from an ester of an oxygenic and nitrogenous organic base molecule.

11. A process as claimed in claim 7 which further comprises desulfurizing the mineral oil or liquid hydrocarbon by a liquid-liquid extraction with a l to 10 percent aqueous alkali-hydrogen sulfide solution in the presence of loo-2,000 ppm of a surface active agent for accelerating the transition of the sulfur from the mineral oil or liquid hydrocarbon to the aqueous phase and recycling the desulfurized mineral oil or liquid hydrocarbon.

12. A process as claimed in claim 11 wherein the aqueous alkali hydrogen sulfide solution has a concentration of 2 to 5 percent and 5001 ,200 ppm of the surface active agent are used.

13. A process as claimed in claim 12 wherein the alkali hydrogen sulfide is NHJ-IS and/or NaHS and the surface active agent is an ionic or nonionic hydroxyalkylate based on a glycol and an alkyleneoxide or a sulfo acid from an ester of an oxygenic and nitrogenous organic base molecule. 

2. A process as claimed in claim 1 wherein the natural gas ascends from the well bottom at the rate of 5,000-15,000 Nm3/hr.
 3. A process as claimed in claim 1 wherein the viscosity is 10-60cP at 20*C.
 4. A process as claimed in claim 1 wherein the amount of mineral oil or liquid hydrocarbon is 500 to 1,000 liters/hr.
 5. A process as claimed in claim 1 wherein the mineral oil is diesel oil, spindle oil or light machine oil and the liquid hydrocarbon is benzene, toluene, xylene, or coal tar oil.
 6. A process as claimed in claim 1 wherein the natural gas contains as much as 5gm of elemental sulfur per Nm3.
 7. A process as claimed in claim 1 wherein the natural gas ascends from the well bottom at the rate of about 10,000 Nm3/hr at a mean gas flow pressure of about 150-500 atm and the ratio of mineral oil to natural gas is about 1 to 20 when the natural gas contains up to about 0.1gm of elemental sulfur per Nm3; the ratio is about 1 to 12 when the natural gas contains about 0.1 to 1.0gm of elemental sulfur per Nm3; the ratio is about 1 to 8 when the natural gaS contains about 1 to 2 gm of elemental sulfur per Nm3 and the ratio is about 1 to 4 when the natural gas contains about 2 to 5gm of elemental sulfur per Nm3.
 8. A process as claimed in claim 1 which further comprises desulfurizing the mineral oil or liquid hydrocarbon by a liquid-liquid extraction with a 1 to 10 percent aqueous alkali-hydrogen sulfide solution in the presence of 100-2,000 ppm of a surface active agent for accelerating the transfer of the sulfur from the mineral oil or liquid-hydrocarbon to the aqueous phase and recycling the desulfurized mineral oil or liquid hydrocarbon.
 9. A process as claimed in claim 8 wherein the aqueous alkali hydrogen sulfide solution has concentration of 2 to 5 percent and 500-1,200 ppm of the surface active agent are used.
 10. A process as claimed in claim 9 wherein the alkali hydrogen sulfide is NH4HS and/or NaHS and the surface active agent is an ionic or nonionic hydroxylakylate based on a glycol and an alkyleneoxide or a sulfo acid from an ester of an oxygenic and nitrogenous organic base molecule.
 11. A process as claimed in claim 7 which further comprises desulfurizing the mineral oil or liquid hydrocarbon by a liquid-liquid extraction with a 1 to 10 percent aqueous alkali-hydrogen sulfide solution in the presence of 100-2,000 ppm of a surface active agent for accelerating the transition of the sulfur from the mineral oil or liquid hydrocarbon to the aqueous phase and recycling the desulfurized mineral oil or liquid hydrocarbon.
 12. A process as claimed in claim 11 wherein the aqueous alkali hydrogen sulfide solution has a concentration of 2 to 5 percent and 500-1,200 ppm of the surface active agent are used.
 13. A process as claimed in claim 12 wherein the alkali hydrogen sulfide is NH4HS and/or NaHS and the surface active agent is an ionic or nonionic hydroxyalkylate based on a glycol and an alkyleneoxide or a sulfo acid from an ester of an oxygenic and nitrogenous organic base molecule. 